The present invention relates to a portable electric apparatus having a main apparatus unit and a detachable power source unit. More particularly, the present invention relates to a radio telephone having a removable rechargeable battery pack, wherein means are provided for preventing the battery pack from accidentally being detached from the radio telephone as well as for preventing the generation of a spark in an explosive environment.
In contemporary radio telephones, such as cellular or mobile telephone, the battery pack is attached to the telephone by means of mechanical fastening members, such as screws, snap-in locking members, etc. Such mechanical fastening members are only provided for securing the battery pack to the telephone; they play no part in establishing electric connection between the battery pack and the telephone for supplying electric power from the former to the latter. On the contrary, separate connecting elements are provided for establishing such electric connection. A common approach is to design the connecting elements as resilient pins, which are screwed, glued or otherwise secured to either the telephone or the battery pack and are arranged to reach electric connection with corresponding contact surfaces provided on the opposite device (telephone or battery).
The fastening members are located separately from the connecting elements. Hence, mounting holes have to be made and threaded for the fastening members as well as for the connecting elements. Furthermore, current losses at about 3% occur at each connecting element and have to be compensated for.
Consequently, for a telephone design according to the above, the production thereof is costly, time-consuming and complicated. Additionally, the connecting elements and the fastening members involve separate material costs.
An important problem is the risk of explosion or fire due to an accidental spark generation at any of the connecting elements when detaching the battery from the telephone. If for instance hydrogen gas has escaped from the battery and joined the airborne oxygen, thereby forming an explosive oxyhydrogen gas, there is an apparent risk of having an explosion due to sparking at the connecting elements. Furthermore, another inflammable gas, such as gasoline fumes at a gas station, may be ignited by such sparking and cause a dangerous explosion and/or fire.
Another disadvantage related to the prior art design described above is that the battery pack will sometimes unintentionally be detached from the telephone, when exposed to external influence, such as punches or vibrations.
It is an object of the present invention to eliminate the drawbacks described above and simplify the detachment of the battery. Furthermore, it is an object of the present invention to provide for improved safety, so that explosive or inflammable gases are prevented from exploding due to accidental sparking when detaching the battery.
In particular, the objects are achieved for a portable electric apparatus having a main apparatus unit and a detachable power source unit, by providing first and second externally operable fastening members having respective first and second connecting elements for mechanically securing and electrically connecting the main apparatus unit to the power source unit. The first and second fastening members are arranged, so that both of them must be externally actuated, by a user of the portable electric apparatus, before the power source unit may be mechanically detached from the main apparatus unit.
Because of the invention, a battery pack may be securely attached to a radio telephone by the provision of double fastening members, which have a combined function for mechanically securing the battery pack as well as electrically connecting the battery pack to the main part of the telephone. According to a preferred embodiment, the fastening members are provided with resilient engagement arms, which are movably mounted in the radio telephone at the rear surface thereof, or alternatively in the battery itself. The engagement arms are in turn connected to respective actuators, such as buttons, tilting levers etc, which must be operated simultaneously in order to release one end of the battery pack from the radio telephone, thereby allowing the battery pack to be detached from the telephone.
According to a preferred embodiment of the invention, the engagement arms are made electrically conductive by means of a respective connecting element provided at each engagement arm. The electrical power losses may be minimized, since the current will be conducted directly from the battery to the connecting elements without any intermediate contacts in the telephone. Thanks to the invention, the battery cannot be detached by only operating one of the actuators and the corresponding engagement arm, since the other engagement arm will maintain the batter in its secured position relative to the telephone. Any sparking generated, when the electrical connection is interrupted between the battery and the telephone, will not reach any possibly inflammable gas outside the battery, thanks to a seal between the battery and the telephone, which seal will fully enclose such sparking. Since both actuators must have been operated in order to detach the battery, a possible sparking will already have occurred, when the battery is detached, and consequently there is not risk of contact between an inflammable gas and a spark generated at any of the connecting elements.
The invention has an important advantage in aforesaid fastening members, which act as electric connecting elements as well as mechanical engagement arms, since assembly costs and material expenses may be reduced. As another important advantage, the battery will be mechanically secured and electrically connected to the telephone at the same positions. Furthermore, the securing arrangement will prevent accidental battery detachment due to e.g. vibrations or punches, since both fastening members must be operated, before the battery is detached.